Increased renal production of C-type natriuretic peptide (CNP) in patients with cirrhosis and functional renal failure.

BACKGROUND/AIMS C-type natriuretic peptide (CNP), the third member of the natriuretic peptide family, is considered to be involved in the regulation of vascular tone. Furthermore, the recent demonstration of CNP in human kidney and urine may indicate a role for CNP in fluid and electrolyte homeostasis. Therefore, the aim of the present study was to investigate the possible role of CNP in renal function disturbances in patients with cirrhosis of the liver. METHODS Peripheral venous and urinary concentrations of CNP were determined in samples from 11 healthy controls, 20 cirrhotic patients with normal renal function (creatinine clearance 117 (8) ml/min), and 20 cirrhotic patients with impaired renal function (creatinine clearance 35 (4) ml/min). In a second protocol, arterial and renal venous plasma concentrations of CNP were determined in 37 patients with cirrhosis of the liver to estimate renal extraction ratios of CNP. A sensitive and specific radioimmunoassay was applied after solid phase extraction of samples. RESULTS Plasma CNP was lower in cirrhotic patients with normal and impaired renal function than in controls (3.0 (0.4) and 2.7 (0.2) v. 4.2 (0.4) pg/ml, respectively; p<0.05; mean (SEM)). In contrast, urinary CNP was higher in patients with impaired renal function compared with those with normal renal function and healthy controls (47.2 (7.4) v. 20.8 (1.9) and 17.0 (3.0) ng CNP/g creatinine, respectively; p<0.05). Urinary CNP was found to be inversely related to urinary sodium excretion in cirrhotic patients (r=-0.56; p<0.01). No differences were observed between arterial and renal venous concentrations of CNP in cirrhosis (2.4 (0.2) v. 2.4 (0.2) pg/ml). In cirrhotic patients with hepatorenal syndrome or refractory ascites (n=5), urinary CNP decreased from 132 (59) to 38 (7) ng/g creatinine (p<0.05) one week after either ornipressin infusion or insertion of a transjugular intrahepatic portosystemic shunt together with an increase in urinary sodium excretion from 27 (17) to 90 (34) mmol/24 hours. CONCLUSIONS Increased urinary CNP in cirrhotic patients in the absence of renal arteriovenous concentration gradients suggests enhanced renal CNP production in cirrhosis. Furthermore, an inverse relation between urinary CNP and urinary sodium excretion suggests a role for this peptide in renal sodium handling in patients with cirrhosis.